In a tooth damaged by caries or the like, when the damage is a relatively small cavity at an initial to middle stage, the cavity is often directly repaired with a composite resin in terms of esthetics, and the simplicity and rapidity of an operation. On the other hand, in the case of the repair of a relatively large cavity, the tooth is covered with a prosthesis made of a metal, a ceramic, or a dental resin via a resin cement. Various dental repairing materials to be used for various purposes such as the composite resin and the resin cement have been proposed (for example, Patent Literature 1).
A dental curable composition containing a radically polymerizable monomer such as a methacrylate-based polymerizable monomer as a main component is typically used as any such dental repairing material, e.g., the composite resin or the resin cement. In addition, the radically polymerizable monomer itself typically has no adhesive property to the tooth, and hence the dental curable composition containing the radically polymerizable monomer as a main component originally has a small adhesive force to the tooth. Accordingly, when the adhesive force between the dental curable composition and the tooth is weak, it becomes difficult to maintain the state of adhesion between the dental curable composition and the tooth owing to a polymerization shrinkage stress caused at the time of its curing.
Meanwhile, the hard tissue of the tooth is formed of enamel and dentin, and hence adhesive properties to both the enamel and the dentin are clinically required. Accordingly, the following method has heretofore been employed. The dental curable composition containing the radically polymerizable monomer as a main component is bonded to the tooth via a bonding material, and the surface of a tooth is pretreated prior to the application of the bonding material in order that the adhesive property of the bonding material to the tooth may be improved. A pretreating material to be used in such pretreatment of the tooth is generally an acid aqueous solution that decalcifies the surface of the tooth, and an aqueous solution of an acid such as phosphoric acid has been used. The mechanism via which the bonding material is bonded to the pretreated surface is said to be: such macroscopic mechanical fitting that the bonding material penetrates a surface roughened by etching with the acid aqueous solution and then cures in (1) the case where the hard tissue of the tooth is the enamel; or such microscopic mechanical fitting that the bonding material penetrates a fine void of a spongy collagen fiber exposed to the surface of the tooth after the decalcification and then cures in (2) the case where the hard tissue of the tooth is the dentin.
However, the penetration of the bonding material into the collagen fiber is not as easy as the penetration of the bonding material into the surface of the enamel. Accordingly, in consideration of the securement of adhesive property not only to the enamel but also to the dentin, etching treatment involving using the acid aqueous solution and primer treatment involving using a penetration enhancer called a primer are generally performed in the stated order prior to the use of the bonding material. That is, an operation in the case where the dental curable composition containing the radically polymerizable monomer as a main component is used has been a three-step system requiring two-stage pretreatment before the application of the bonding material for obtaining good adhesive strengths to both the enamel and the dentin. Accordingly, a problem in that the operation is complicated has arisen.
In view of the foregoing, in recent years, the following two-step system has been proposed for simplifying the operation of clinical therapy (see Patent Literature 2). Treatment involving using a self-etching primer that performs such etching treatment and primer treatment as described above at the same time, and treatment for applying the bonding material are performed in the stated order, and then the dental curable composition is bonded to the tooth. The following one-step system has also been proposed (self-bonding treatment, see Patent Literature 3). After treatment for applying a bonding material (self-etching bonding material) that does not require pretreatment such as the etching treatment or the primer treatment, the dental curable composition is bonded to the tooth.
Further, studies have been made on the following self-adhesive composite resin or self-adhesive resin cement. Even when a cavity is filled with the composite resin or the tooth is covered with a prosthesis via the resin cement, the composite resin or the resin cement does not require pretreatment such as the etching treatment or the primer treatment and treatment for applying the bonding material, and is directly bonded to the tooth. It should be noted that each of the related-art dental adhesive compositions such as the self-etching primer, the self-etching bonding material, the self-adhesive composite resin, and the self-adhesive resin cement contains an acidic group-containing polymerizable monomer as a main component, and has a self-etching function and adhesive property.